Fatigue strength of hybrid welded 22MnB5 overlap joints

Helge Kügler; Felix Möller; Sven-Frithjof Goecke; Frank Vollertsen

doi:10.3139/120.110880

Published by De Gruyter May 23, 2016

Fatigue strength of hybrid welded 22MnB5 overlap joints

Dauerfestigkeit hybridgeschweißter Überlappnähte des Stahls 22MnB5

Helge Kügler , Felix Möller , Sven-Frithjof Goecke and Frank Vollertsen

From the journal Materials Testing

https://doi.org/10.3139/120.110880

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Abstract

In order to reduce the weight of automotive parts, lightweight materials like the press hardened AlSi coated high strength steel 22MnB5 is used. This steel enables a reduction of wall thicknesses and simultaneously ensures a high stiffness of the part, e. g., the B pillar. The usage of these steels requires suitable joining technologies. Therefore, a laser GMA hybrid welding process for fillet welds in overlap configuration was designed. This process provides high welding velocities and process tolerances against gaps and misalignments. In this case a single-mode fiber laser was used in order to reduce the thermal impact. Due to the fact that the laser focus spot has only a small diameter of 25 µm, a beam oscillation was used in order to distribute the laser energy over the melt pool width. This paper is focused on the cyclic load tests which were carried out and analyzed by the staircase method. The influences of laser power and oscillation width are dominating, whereas welding velocity and wire velocity have only a minor influence. By analyzing the failure location and crack propagation of specimens after the cyclic load test, the influence of the AlSi coating can be determined. Coating agglomerations at the fusion line of the melt pool are origins of crack initiation. This is attributed to the formation of brittle intermetallic phases.

Kurzfassung

Zur Gewichtsreduktion von Automobilteilen werden Leichtbauwerkstoffe wie der pressgehärtete hochfeste Stahl 22MnB5 mit AlSi-Beschichtung verwendet. Dieser Stahl ermöglicht eine Reduzierung der Wandstärken und gewährleistet gleichzeitig eine hohe Bauteilsteifigkeit, z. B. der B-Säule. Die Verwendung dieser Stähle erfordert geeignete Fügetechnologien. Aus diesem Grund wurde ein Laser-MSG-Hybridschweißprozess für Kehlnähte als Überlappkonfiiguration entwickelt. Dieses Verfahren liefert hohe Schweißgeschwindigkeiten und Prozesstoleranzen hinsichtlich Nahtüberbrückungen und Kantenversatz. In diesem Fall wurde ein Single-Mode-Faserlaser verwendet, um die thermische Belastung zu verringern. Da der Laserfokus einen kleinen Durchmesser von 25 µm aufweist, wurde eine Strahloszillation verwendet, um die Energie des Lasers über die Breite des Schmelzbades zu verteilen. Diese Veröffentlichung konzentriert sich auf Lastwechselversuche, die mit dem Stufenverfahren durchgeführt und analysiert wurden. Die Einflüsse der Laserleistung und Schwingungsbreite dominieren, während Schweißgeschwindigkeit und Drahtgeschwindigkeit nur einen geringen Einfluss haben. Durch die Analyse der Bruchstelle und Rissausbreitung nach dem Lastwechselversuch konnte der Einfluss der AlSi-Beschichtung bestimmt werden. Beschichtungsanhäufungen an der Schmelzlinie des Schmelzbades sind ursächlich für die Rissinitiierung. Dies ist auf die Bildung spröder intermetallischer Phasen zurückzuführen.

*Correspondence Address, Prof. Dr.-Ing. S.-F. Goecke, Fachhochschule Brandenburg Magdeburger Straße 50, 14770 Brandenburg an der Havel, Germany. E-mail: goecke@TH-Brandenburg

** M. Sc. Helge Kügler, Schweißfachingenieur (IWE), Gruppenleiter Fügeprozesse, BIAS – Bremer Institut für angewandte Strahltechnik GmbH, Klagenfurter Straße 2, 28359 Bremen, Germany. E-mail: kuegler@bias.de

M.Sc. IWE Helge Kügler studied Mechanical Engineering at Jade HS in Wilhelmshaven, Germany and Production Engineering at University of Bremen, Germany, where he received his MSc. Since October 2012 he is a research associate at BIAS – Bremer Institut für Angewandte Strahltechnik GmbH, Germany. Since December 2015 he is in charge of the group Joining Processes.

Felix Möller graduated in the field of Physical Engineering at University of Applied Science in Gelsenkirchen, Germany, where he received his MSc. He was awarded with the Master Degree studying Production Engineering at University of Bremen, Germany. From October 2011 to November 2015, he was in charge of the group Joining Processes at BIAS – Bremer Institut fürr Angewandte Strahltechnik GmbH, Germany. Since December 2015 he is employed at the welding machine manufacturing company Hugo Miebach GmbH in Dortmund, Germany.

Prof. Dr.-Ing. Sven-Frithjof Goecke studied Mechanical Engineering and Drive Engineering at TU Berlin, Germany. From 1991 to 1992, he was in charge of the Airbus industry project “Aerospace Passenger Emergency Oxygen Systems”. From 1993 to 2004, he was a scientific assistant and a joint research project coordinator at TU Berlin. He recieved his PhD in the field of welding technology in 2004. From 2004 to 2009, he was the Head of R & D at EWM Hightec Welding GmbH, Mündersbach, Germany. Since 2009 he is Professor for Manufacturing and Production Engineering, Technical University of Applied Sciences TH Brandenburg, Germany.

Prof. Dr.-Ing. Frank Vollertsen studied Material Science in Erlangen, Germany. He received his PhD and habilitated in the field of production engineering. From 1998 to 2002, he was Professor at the Department for Metal Forming Technologies (LUF) at the University of Paderborn, Germany. Since 2003 he is the CEO of BIAS – Bremer Institut für Angewandte Strahltechnik GmbH, Germany, and Professor in the Department of Welding and Related Processes at the University of Bremen, Germany.

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Published Online: 2016-05-23

Published in Print: 2016-06-01

Fatigue strength of hybrid welded 22MnB5 overlap joints

Abstract

Kurzfassung

References

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